Jun
09

Waterthrushes and Gummy Bears

By

vieill type of Louisiana waterthrusy

Waterthrush identification and misidentification can lay bare some strong emotions. In a recent online discussion of the value of the color of the supercilium, one of North America’s best birders was moved to this outburst:

the first individual to propose [that character as a useful distinction] should be covered in honey and gummy bears and thrown to a ravaging class of preschoolers to receive their just deserts.

As soon as I’d stopped laughing out loud, I silently congratulated Cameron for knowing the phrase “just deserts” (and spelling it right!), and then, inevitably, started to wonder: just who might that sticky-fated “first individual” have been?

Pl enl 752 labeled tachetée

This particular ID chestnut turns out to be older than I’d expected. I knew that Roger Tory Peterson had used the color of the supercilium to distinguish the two species as early as the first Field Guide of 1934, and it was an easy matter to confirm that in this he was following the great Ralph Hoffman, who had written a quarter of a century before — in italics — that the Louisiana was to “be distinguished by the pure white line over the eye,” the same part of the bird “buffy in a strong light” in the northern waterthrush.

We have to go back another sixty years beyond that, though, to find what I believe is the first authoritative statement of the importance of supercilium color in identifying the waterthrushes. In 1858, Spencer Baird and his colleagues at the Smithsonian informed their readers that the Louisiana waterthrush was “readily distinguished” from its more widespread congener by its large bill and by the fact that

the stripe over the eye, besides being more conspicuous, is, with the underparts, of a decided white, instead of brownish yellow,

as in the northern. Baird, Brewer, and Ridgway would reaffirm this “field mark” in their influential History of North American Birds, published in 1874, this time reinforcing its validity in the accompanying color plate.

Ridgway 1874 waterthrushes

Before 1858, every published source seems to have relied on bill and tarsus measurements to distinguish the two species. And so the famous trio — the Nestor of American ornithology, the father of American oology, and the great cataloguer of American birds — appears to be responsible for promulgating the notion that the color of the eye stripe is sufficient to separate the brown-crowned members of the genus Parkesia. 

There we have it. Break out the honey, prepare the gummy bears, rally the preschoolers!

More about the tangled history of these species to come — 

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